fix: wire S4 validation, fix tier phase labels, iterative cooldown drain

wip: S4 rapid transition validation (Task 10, partial)

feat(tuner): hardening pipeline — post-confirm multi-mode stress tiers

feat(tuner): crash-aware scheduling — cooldown and crash history

feat(tuner): pre-crash safety ramp near max_offset

feat(tuner): death spiral prevention via time budget

feat(tuner): crash detection on resume with penalty backoff

feat(export): tuner profile export/import with validation

feat(db): schema v9 — crash tracking, hardening tier, backend info on test log

feat(tuner): add hardening_tiers, time budget, crash penalty config options

feat(tuner): add hardening phases and crash tracking fields to state machine

docs: multi-mode tuning pipeline spec and implementation plan

docs: update README for backend registry, phase enum, encoding schemes

refactor: DX improvements — backend registry, phase enum, encoding schemes, migration system

harden: thread-safe SMU commands, scheduler locks, MCE drain